This invention relates to novel substituted pyrrolidine compounds and derivatives thereof useful as neuraminidase inhibitors, to pharmaceutical compositions containing said compounds useful for the prevention, treatment or amelioration of viral, bacterial and other infections, and to methods of using said compounds. The present invention is also concerned with novel intermediates or precursors for producing the novel substituted pyrrolidine compounds of the present invention.
Despite the wealth of information available, influenza go remains a potentially devastating disease of man, lower mammals, and birds. No effective vaccine exists and no cure is available once the infection has been initiated.
Influenza viruses consist of eight pieces of single stranded is RNA, packaged in orderly fashion within the virion. Each piece codes for one of the major viral proteins. The replication complex is enclosed with a membrane composed of matrix protein associated with a lipid bilayer. Embedded in the lipid bilayer are two surface glycoprotein spikes, hemagglutinin (HA) and the enzyme neuraminidase (NA). All of the viral genes have been cloned and the three-dimensional structures of the surface glycoproteins have been determined.
Influenza viruses continually undergo antigenic variation in the two surface antigens, HA and NA, toward which neutralizing antibodies are directed. For this reason, vaccines and a subject""s natural immune system have not been very effective. Attention is now being directed to finding other potential antiviral agents acting at other sites of the virion. This invention is directed to novel compounds which are useful in inhibiting the viral surface enzyme NA.
Furthermore, many other organisms carry NA. Many of these NA-possessing organisms are also major pathogens of man and/or mammals, including Vibraeo cholerae, Clostridium perfringes, Streptococcus pneumonia, Arthrobacter sialophilas, and other viruses, such as parainfluenza virus, mumps virus, Newcastle disease virus, fowl plague virus, and Sendai virus. Compounds of this invention are also directed to inhibiting NA of these organisms.
In viruses, NA exists as a tetramer made of four roughly spherical subunits and a centrally-attached stalk containing a hydrophobic region by which it is embedded in the organism""s membrane. Several roles have been suggested for NA. The enzyme catalyzes cleavage of the xcex1-ketosidic linkage between terminal sialic acid and an adjacent sugar residue. Removal of the sialic acid lowers the viscosity and permits access of the virus to the epithelial cells. NA also destroys the HA receptor on the host cell, thus allowing elution of progeny virus particles from infected cells.
Research indicates that the active site for influenza neuraminidase remains substantially unchanged for the major strains of influenza. For example, a comparison of sequences from influenza A subtypes and influenza B shows conserved residues with crucial structural and functional roles. Even though the sequence homology is only about 30%, many of the catalytic residues are conserved. Furthermore, the three-dimensional structures of influenza A and B neuraminidases have been determined. Superposition of the various structures shows remarkable structural similarity of the active site. Since the active site amino acid residues are conserved in all known influenza A neuraminidases that have been sequenced so far, an inhibitor that is effective against different strains of influenza A and/or B neuraminidase can be designed based on the three-dimensional structure of a neuraminidase.
In general, the role of NA is thought to be for the mobility of the virus both to and from the site of infections. Compounds that inhibit neuraminidase""s activity may protect a subject from infection and/or cure a subject once infection has set in. It is a further object of this invention to provide a method of using compounds of this invention for treating and/or curing a viral infection.
Analogs of neuraminic acid, such as 2-deoxy-2,3-didehydro-N-acetylneuraminic acid (DANA) and its derivatives are known to inhibit NA in vitro; however, these compounds are inactive in vivo. Palese and Schulman, in CHEMOPROPHYLAXIS AND VIRUS INFECTION OF THE UPPER RESPIRATORY TRACT, Vol. 1 (J.S. Oxford, Ed.), CRC Press, 1977, at PS 189-205.
Von Itzstein et al. describes cyclohexane analogs of xcex1-D-neuraminic acid of the formula 
wherein:
A is, O, C or S in Formula (a), and N or C in Formula (b);
R1 is CO2H, PO3H2, NO2, SO2H, SO3H, tetrazolyl-, CH2CHO, CHO, or CH(CHO)2;
R2 is H, OR6, F, Cl, Br, CN, NHR6, SR6 or CH2X, where X is NHR6 halogen, or OR6;
R3 and R3, are H, CN, NHR6, SR6, xe2x95x90NOR6, OR6, guanidino, NR6;
R4 is NHR6, SR6, OR6, CO2R6, NO2, C(R6)3, CH2CO2R6, CH2NO2 or CH2NHR6;
R5 is CH2YR6, CHYR6CH2YR6 or CHYR6CHYR6CH2YR6;
R6 is H, acyl, alkyl, allyl, or aryl;
Y is O, S, NH, or H;
and pharmaceutical salts thereof, useful as antiviral agents.
In addition, certain benzene derivatives are suggested in U.S. Pat. No. 5,453,533 as being inhibitors of influenza virus neuraminidase and various others are disclosed in U.S. Pat. No. 5,602,277. Yamamoto et al. describe various sialic acid isomers as having inhibitory activity against neuraminidase in Synthesis of Sialic Acid Isomers With Inhibitory Activity Against Neuramninidase, TETRAHEDRON LETTERS, Vol. 33, No. 39, pp. 5791-5794, 1992.
WO 96/26933 to Gilead Sciences, Inc. describes certain 6-membered ring compounds as possible inhibitors of neuraminidase.
WO 98/17647 to Gilead Sciences, Inc. describes certain 6-membered piperidine compounds as possible inhibitors of neuraminidase.
Hoff et al suggest that certain N-aryl xcex1-pyrrolidinones are useful as intermediates for dyes and pharmaceuticals, as reported in Chemical Abstracts, Vol. 52, Item 11124g, 1958.
However, none of these references disclose the pyrrolidine derivatives of the present invention.
The present invention relates to certain substituted pyrrolidine compounds. More particularly, the compounds of the present invention are selected from the group consisting of the following formulae:
wherein 
wherein
Z is xe2x80x94C(R2)(R3), xe2x80x94CHxe2x80x94N(R2)(R3), C(R3)[(CH2)nR2], or CHxe2x80x94C(R3)(CH2)nR2;
R1 is H, (CH2)nOH, (CH2)nNH2, (CH2)nNR10R11, (CH2)nOR11, or (CH2)nF;
R9 is (CH2)nCO2H, (CH2)nSO3H, (CH2)nPO3H2, (CH2)nNO2, esters thereof, or salts thereof;
R2 is H, NHC(O)R5, NHC(S)R5, NHSO2R5, C(O)NHR5, SO2NHR5, CH2S(O)R5, or CH2SO2R5;
R3 is H, (CH2)nCO2R10, (CH2)mOR10, C(O)N(R10)m, (CH2)nN(R10)m, CH(R10)m, (CH2)n(R10)m, CH2CH(OR10)CH2OR10, CH(OR10)CH(OR10)CH2OR10, CH2OR10, CH(OR10)CH2NHR10, CH2CH(OR10)CH2NHR10, CH(OR10)CH(OR10)CH2NHR10, C(xe2x95x90NR10)N(R10)m, NHR10, or NHC(xe2x95x90NR10)N(R10)m;
R4 is H, (CH2)nOH, (CH2)nNR10R11, (CH2)nNH2, (CH2)nC(xe2x95x90NH)(NH2), (CH2)nR10R11, (CH2)nNHC(xe2x95x90NR11)NH2, (CH2)nNHC(xe2x95x90NR7)NH2, (CH2)nCN, (CH2)nN3, C(xe2x95x90NH)NH2, C(NR7)NH2, or C(NR11)NH2;
R5 is H, lower alkyl, lower branched chain alkyl, cyclic alkyl, halogen substituted alkyl, aryl, substituted aryl, or CF3;
R7 is H, (CH2)nOH, (CH2)nCN, (CH2)nNH2, or (CH2)nNO2;
R10 is H, lower alkyl, lower alkylene, lower branched alkyl, cyclic alkyl, (CH2)n aromatic, (CH2)n substituted aromatic, or when m is 2 both R10 groups can also be interconnected to form an N substituted heterocyclic ring, or other 5 or 6 membered heterocyclic ring;
R11 is lower alkyl, lower branched alkyl, or (CH2)m aromatic;
R13 is H, (CH2)nOH, (CH2)nNH2, (CH2)nNR10R11, (CH2)nOR11, (CH2)nF, (CH2)nOC(O)R11, or (CH2)nNHC(O)R11;
m is 1 or 2;
n is 0-4;
and pharmaceutically acceptable salts thereof.
The present invention is also concerned with compositions for inhibiting influenza virus neuraminidase comprising a pharmaceutically acceptable carrier and an amount effective for inhibiting influenza virus neuraminidase of a compound as defined above.
A further aspect of the present invention involves a method for inhibiting influenza virus that comprises administering to a patient in need thereof a compound as defined above in an amount effective for inhibiting influenza virus neuraminidase.
A still further aspect of the present invention is concerned with treating influenza virus infection comprising administering to a patient in need thereof a compound as defined above in an amount effective for inhibiting influenza virus neuraminidase.
The present invention is also concerned with methods for producing the compounds defined above.
The present invention relates to certain pyrrolidine compounds. More especially, the compounds of the present invention are selected from the group consisting of the following formulae: 
and pharmaceutically acceptable salts thereof; and wherein
Z is xe2x80x94C(R2)(R3), xe2x80x94CHxe2x80x94N(R2)(R3), C(R3)[(CH2)nR2], or CHxe2x80x94C(R3)(CH2)nR2;
R1 is H, (CH2)nOH, (CH2)nNH2, (CH2)nNR10R11, (CH2)nOR11, or (CH2)nF;
R9 is (CH2)nCO2H, (CH2)nSO3H, (CH2)nPO3H2, (CH2)nNO2, esters thereof, or salts thereof;
R2 is H, NHC(O)R5, NHC(S)R5, NHSO2R5, C(O)NHR5, SO2NHR5, CH2S(O)R5, or CH2SO2R5;
R3 is H, (CH2)nCO2R10, (CH2)mOR10, C(O)N(R10)m, (CH2)nN(R10)m, CH(R10)m, (CH2)n(R10)m, CH2CH(OR10)CH2OR10, CH(OR10)CH(OR10)CH2OR10, CH2OR10, CH(OR10)CH2NHR10, CH2CH(OR10)CH2NHR10, CH(OR10)CH(OR10)CH2NHR10, C(xe2x95x90NR10)N(R10)m, NHR10, or NHC(xe2x95x90NR10)N(R10)m;
R4 is H, (CH2)nOH, (CH2)nNR10R11, (CH2)nNH2, (CH2)nC(xe2x95x90NH)(NH2), (CH2)nR10R11, (CH2) nNHC(xe2x95x90NR11)NH2, (CH2)nNHC(xe2x95x90NR7)NH2, (CH2)nCN, (CH2)nN3, C(xe2x95x90NH)NH2, C(NR7)NH2, or C(NR11)NH2;
R5 is H, lower alkyl, lower branched chain alkyl, cyclic alkyl, halogen substituted alkyl, aryl, substituted aryl, or CF3;
R7 is H, (CH2)nOH, (CH2)nCN, (CH2)nNH2, or (CH2)nNO2;
R10 is H, lower alkyl, lower alkylene, lower branched alkyl, cyclic alkyl, (CH2)n aromatic, (CH2)n substituted aromatic, or when m is 2 both R10 groups can also be interconnected to form an N substituted heterocyclic ring, or other 5 or 6 membered heterocyclic ring;
R11 is lower alkyl, lower branched alkyl, or (CH2)m aromatic;
R13 is H, (CH2)nOH, (CH2)nNH2, (CH2)nNR10R11, (CH2)nOR11, (CH2)nF, (CH2)nOC(O)R11, or (CH2)nNHC(O)R11;
m is 1 or 2; and
n is 0-4.
The esters are typically lower alkyl esters having 1 to about 12 carbon atoms and preferably 1 to about 3 carbon atoms and aryl esters containing 6 to 14 carbon atoms. The alkyl esters can be straight-chain, branched-chain or cyclic saturated aliphatic hydrocarbons.
Examples of some alkyl esters are methyl, ethyl, propyl, isopropyl, t-butyl, cyclopentyl and cyclohexyl esters. The aryl esters are preferably phenyl or alkyl substituted aromatic esters (alkaryl) including C1-3 alkyl substituted phenyl such as benzyl.
The alkyl groups typically contain 1 to about 12 carbon, and preferably 1 to about 3 carbon atoms, and can be straight, branched-chain or cyclic saturated aliphatic hydrocarbon groups.
Examples of suitable alkyl groups include methyl, ethyl and propyl. Examples of branched alkyl groups include isopropyl and t-butyl. Examples of suitable cyclic aliphatic groups typically contain 3-8 carbon atoms and include cyclopentyl and cyclohexyl.
Examples of substituted cycloalkyl groups include cyclic aliphatic groups typically containing 3-8 carbon atoms in the ring substituted with alkyl groups typically having 1-6 carbon atoms and/or hydroxy group. Usually 1 or 2 substituted groups are present.
Examples of aryl groups are phenyl and naphthyl. Alkaryl groups typically contain 1-3 carbon atoms in the alkyl group such as benzyl. The alkyl moiety can be linear or branched.
Suitable heterocyclic rings include those containing N, 0 or S atoms and having 5 or 6 members in the ring. Examples include pyrrolidinyl, piperidinyl, morpholinyl, 2- and 3-thienyl, and 2-and 3-furanyl.
Pharmaceutically acceptable salts of the compounds of formula (I) include those derived from pharmaceutically acceptable, inorganic and organic acids and bases. Examples of suitable acids include hydrochloric, hydrobromic, sulphuric, nitric, perchloric, fumaric, maleic, phosphoric, glycollic, lactic, salicyclic, succinic, toluene-p-sulphonic, tartaric, acetic, citric, methanesulphonic, formic, benzoic, malonic, naphthalene-2-sulphonic, trifluoroacetic and benzenesulphonic acids.
Salts derived from appropriate bases include alkali such as sodium and ammonia.
Examples of some specific compounds within the scope of the present invention are:
trans-3-Acetylamino-4-hydroxypyrrolidine-1-acetic acid;
cis-3-Acetylamino-4-hydroxypyrrolidine-1-acetic acid;
trans-3-Acetylamino-4-aminopyrrolidine-1-acetic acid;
trans-3-Acetylamino-4-(aminoiminomethyl)aminopyrrolidine-1-acetic acid;
cis-3-Acetylamino-4-(aminoiminomethyl)aminopyrrolidine-1-acetic acid;
trans-5-(1-Acetylamino-2-ethyl)butyl-1-aminoiminomethylpyrrolidine-3-carboxylic acid.
Compounds according to the present invention can be prepared according to the following schemes: 
As shown in Scheme-5, the cycloaddition reaction of oximino compound 1 [Biehler, J. M; Perchais, J; Fleury, J. P. Bull. Soc. Chim Fr 1971, 7, 2711] with 2-alkoxy-1,3-cyclopentadiene 2 [Wolfgang, K.; Karin, L. Chem. Ber. 1981, 114(1), 400-404 and Mironov, V. A.; Luk""yanov, V. T.; Bernadskii, A, A. Zh. Org. Khim. 1984, 20(10), 69-80] furnishes the azabicyclic compound 3 [Biehler, J. M; Perchais, J; Fleury, J. P. Bull. Soc. Chim Fr 1971, 7, 2711; Biehler, J. M; Perchais, J; Fleury, J. P.; Regent, A. Tetrahedron Lett. 1968, 4277; Fleury, J. P.; Biehler, J. M; Desbois, M. Tetrahedron Lett. 1969, 4091.; Biehler, J. M.; Fluery, J. P. J. Heterocycl. Chem. 1971, 8, 431.; Biehler, J. M.; Fluery, J. P. Tetrahedron. 1971, 27, 3171.; Fluery, J. P. Chemia. 1977, 31, 143. and
Fluery, J. P. Desbois, M.; See, J. Bull. Soc. Chim. Fr. II .1978, 147.] as a mixture of isomers. The required isomer is separated and subjected to decarboxylation when R1 is an ester. When R1 is nitrile the hydrolysis is followed by decarboxylation [Biehler, J. M.; Fluery, J. P. Tetrahedron. 1971, 27, 3171]. The exo and endo isomers of compound 4 are separated at this stage. The deprotection of tosyloxy group in compound 4 is achieved by Na-Hg reduction [Biehler, J. M.; Fluery, J. P. Tetrahedron. 1971, 27, 3171] followed by protection of nitrogen in the azabicyclic system compound 5 as a tert-butoxy carbamate to give compound 6. Reductive alkylation followed by acetylation [Effenberger, F.; Roos, J. Tetrahedron Asym. 2000, 11(5), 1085-1095] provides compound 7. The ozonoylsis [Schill G.; Priester, C.; Windhovel, U.; Fritz, H, Tetrahedron 1987, 43(16), 3765-3786] of compound 7 favors the oxidation to form ester and aldehyde in the required cis configuration in compound 8. The Wittig reaction of compound 8 with appropriate ylide provides the alkene 9, which on hydrolysis of protecting groups furnishes target compound 10. Aldehyde group of 8 may be converted to other groups also, such as, CH2OH, CH2Oalkyl/alkenyl/alkynyl, CO2H, amides, etc. through the standard chemical transformation reactions. 
Scheme-6 takes the advantage of the availability of the optically pure alpha substituted amino acid 1 [Schollkopf, U.; Groth U.; Deng, C. Angew. Chem. Int. Ed. Engl. 1981, 20(11), 798-799. and Schollkopf, U.; Groth U. Angew. Chem. Int. Ed. Engl. 1981, 20(11), 977-978]. The chiral aldehyde 2 obtained from 1 is reacted with urethane 3 to form alkylidenebisurethanes 4, which undergo fragmentation in solution in presence of catalytic amounts of Lewis acid to afford dienophilic N-(alkoxycarbonyl)iminium ion [Sibi M. P. Org. Prep. Proc. Int. 1993, 25(1), 15-40 and Krow, G. R.; Henz, K. J.; Szczepanski, S. W. J. Org. Chem. 1985, 50, 1888-1894]. Thus 2-methoxy-l,3-cyclopentadiene 5 reacts with alkylidenebis(urethane) to furnish the azabicyclo compound 6 with preferential exo stereochemistry. The isomers are separated at this stage and the pure isomer is subjected to oxidation by ozonoylsis [Schill G.; Priester, C.; Windhovel, U.; Fritz, H, Tetrahedron 1987, 43(16), 3765-3786] to furnish compound 8 with the required cis stereochemistry. Further trasformations are the same as described in scheme-5.